Prozinc expired maybe?

My Viggo's has come out of remission after 5 or 6 months, and I am getting a few unexpected numbers on him , like higher at nadir, or higher and he hasn't eaten anything. It occurred to me--this bottle of Prozinc I have been using on him since last March, but it was then not touched from July to this January. Bottle says expires this coming May, but.....perhaps its expiring now??

Yes, the expiration on the bottle is assuming it hasn't been opened. Once opened, the manufacturer says it only lasts about a month. Most of us would say you can use it for about six months. Beyond that though, it's not reliable. I would recommend a new vial, and as Rachel said, any numbers you have would be helpful so we can help you get Viggo into a better place!